1. Field of the Invention
The present invention relates to an optical device such as a zoom lens used in a TV camera, video camera, or the like.
2. Related Background Art
An optical device such as a TV lens or video lens comprises optical adjustment means such as a zoom lens optical system, focus lens optical system, and light quantity adjustment system. Most of optical devices can control the driving velocities of these optical adjustment means.
A zoom switch and zoom demand operated to designate driving of the optical adjustment means are disclosed in, e.g., Japanese Patent Application Laid-Open No. 51-40924. An optical device disclosed in this reference is equipped, for a zoom lens optical system such as a TV lens or video lens, with a servo means constituted by a driving system such as a motor and a control system for controlling the operation of the driving system. This optical device uses a zoom switch and zoom demand in order to supply a command signal to a control system in the servo means.
In actual zoom operation, the user can adjust the zoom velocity to a desired one from a low velocity to a high velocity in accordance with the operation amount of the zoom switch or the thumb ring of the zoom demand.
Image sensing using a TV camera or video camera adopts various image sensing methods, one of which is zooming at a constant velocity (e.g., low velocity). This constant-velocity zooming may be repeated many times during image sensing.
To easily execute constant-velocity zooming, there is an optical device having a function (to be referred to as a speed preset function hereinafter) of driving a zoom lens optical system at a pre-stored driving velocity toward a pre-stored driving direction.
More specifically, while the zoom lens optical system is driven at an arbitrary velocity, a storage designation operation means (memory switch or the like) is operated to store the driving velocity (and driving direction) at that time. Driving of the zoom lens optical system at a driving velocity (and direction) corresponding to the stored preset velocity information is executed in accordance with the operation of a preset drive start operation means (preset switch or the like).
This speed preset function can easily repeat constant-velocity zooming an arbitrary number of times. However, the driving velocity of the zoom lens optical system cannot be adjusted, particularly slightly adjusted during execution of the speed preset function.
A desired driving velocity can be obtained by stopping execution of the speed preset function (e.g., operating the preset drive start operation means again) and performing general zoom operation with a zoom switch or the like. This operation is cumbersome, and the changed velocity is difficult to maintain.
In addition, the preset function can easily repeat constant-velocity zooming an arbitrary number of times, but the zoom lens optical system can only be driven toward a predetermined direction stored in advance. It is, therefore, difficult to employ an image sensing method of driving the zoom lens optical system at a predetermined velocity (low velocity) toward the opposite direction during zooming at the same velocity using the speed preset function.
A desired driving direction can be set by stopping execution of the preset function (e.g., operating the preset drive start operation means again) and performing general zoom operation with the zoom switch or the like. This operation is cumbersome, and the start of reversing the driving direction delays.